The use of supports in motor vehicle seats which can be shaped according to anatomic specifications has been steadily increasing. In addition to supports which allow for a position of the thighs so as to reduce maximum pressure, the so-called lumbar support devices have particular significance. As a result of the preferred forward leaning posture of the seat occupant, the natural, forward concave shape of the lumbar column is replaced by a substantially convex one curved toward the rear, which causes, in addition to quicker fatigue, an undesirable distortion of the intravertebral disks. In order to avoid such an undesirable posture, lumbar supports are provided in motor vehicle seats. Such lumbar support devices must be designed to be adjustable by height in order to fit different back lengths and thus different levels of the lumbar area. Usually, such lumbar support devices are covered by the cushioning of the motor vehicle seat. This cushioning may be filled with foam rubber.
Various technically differently designed lumbar support devices are known. One form provides an inflatable cylinder in the lumbar area. An example of this pneumatic lumbar adjustment is disclosed in U.S. Pat. No. 4,655,505. Multiple air chambers can be controlled sequentially via corresponding valves. The pressure in the air chambers can be decreased by means of an exhaust valve or increased by means of a pumping device, and measured by means of a pressure sensor.
Another lumbar support is designed such that two hinged parts can be moved toward or away from each other along a guide. A variably designed curvature is not possible. As a result, a support for the lumbar area is provided in a narrow range at its highest position only, thereby supporting no more than one or two vertebra. An example of this such a lumbar support is described in WO 95/19123.
Another lumbar support design has a substantially planar support part, whereby the plane is provided either with perforations or individual support elements arranged next to each other. These elements may taper from the middle towards the outside. This planar support part can be moved by moving its two end areas towards each other, such that a curvature thereof may be obtained. By forming different thicknesses according to EP 0 698 360 B, a desired asymmetric shape that substantially corresponds to a lumbar curve can be achieved.
As a rule, the above cited lumbar support devices are connected to a frame, for example the back part of a car seat. In that embodiment, the support part of the lumbar support is connected to an additional frame that has two external supports running substantially parallel to the spinal column, along which gliding elements are moveable or to which lateral supports for a curvable support part are stationarily attached.
From WO 95/191123 a lumbar support is known that is not provided with a curvable support part but with two arms hinged to each other. The ends of the arm parts can be moved relative to each other and the other ends are connected via a rail with two cylindrical recesses.
In addition to manual adjustment of such lumbar support devices (also called spinal supports or lordotic supports), electrically or pneumatically adjustable lumbar support adjustment devices are known that allow for the electrically controlled setting of a desired shape. These electrically controlled adjustments are operated, for example, by a button or a switch. The adjustment in said lumbar supports depends on their mechanical design.
Such electrical control of a lumbar adjustment device is known from DE 43 13 757 A1 and U.S. Pat. No. 5,243,267. The electrical control enables the obtaining of a massage effect by means of a motor repeatedly effecting a back-and-forth movement of the lumbar plate within a predefined time frame, in addition to the manual control of the desired support position.